Decorative laminates whose base surfaces are decorated with patterns or the like by a direct printing, laminating or transfer printing method, or the like, have conventionally been used for various uses. In such decorative laminates, the surfaces of the bases can easily be decorated with patterns when they are flat; however, patterns have been formed by special means when the surfaces have irregularities.
For instance, one of curved-surface-decorating techniques which can be applied to a case where base surfaces to be decorated are columnar and have two-dimensional irregularities [a shape having curvature in only one direction (in the direction perpendicular to the direction of generatrix or of height) like that of a column] such as Japanese Patent Publication No. 61-5895. Namely, the technique described in the above patent publication is a surface-decorating technique utilizing a laminating method which comprises feeding a decorative sheet whose one surface has been coated with an adhesive; horizontally carrying a base at a speed which is synchronized with the speed at which the decorative sheet is feed; pressing stepwise every small area of the decorative sheet against the base with the adhesive-coated surface of the decorative sheet facing the base, while maintaining by a large number of presser jigs juxtaposed in such a condition that the end of the decorative sheet is not adhered; and thermally adhering the decorative sheet to the surface of the base. This method is called a lapping method.
A curved-surface-decorating techniques applicable to a case where surface irregularities are three dimensional like those on embossed surfaces (i.e., a shape having curvature in two directions like that of a hemispheric surface) is proposed, for example, in Japanese Patent Laid-Open Publication No. 5-139097. Namely, the technique described in this patent publication is a surface-decorating method employing a transfer printing method in which a thermoplastic resin film is used as the substrate of a transfer printing sheet and which comprises placing, on a base having a convexly curved surface, a transfer printing sheet prepared by successively forming a release layer, a pattern layer and an adhesive layer on the substrate, and pressure the transfer printing sheet by a heated roll made of rubber having a rubber hardness of 60.degree. or less from the back surface of the substrate to transfer the pattern to the base, thereby obtaining a decorative laminate. Further, an expandable layer which expands by heat applied thereto when transfer printing is conducted is provided between the substrate and the release layer. In this method, the expansion of this layer is also utilized to closely fit the transfer printing sheet to the irregular surface of the base.
However, among the above-described conventional methods, the method disclosed in Japanese Patent Publication No. 61-5895 can cope with, at most, two-dimensional curved surfaces; and the method proposed in Japanese Patent Laid-Open Publication No. 5-139097 can cope with three-dimensional curved surfaces, and is applicable to embossed configurations with small depths, but not applicable to large surface irregularities because the elastic deformation of the rubber of the rotating heated roll is basically utilized to closely fit the transfer printing sheet to surface irregularities. In addition, the roll made of soft rubber tends to be abraded by the corners of irregularities present on the transfer-printing-pattern-receiving base. Moreover, in the case of the configuration in which an expandable layer is provided on a transfer printing sheet, such a transfer printing sheet becomes complicated and excessively expensive. Further, transfer printing can be conducted only on flat-plate-like bases. Furthermore, in the above-described conventional techniques, a heated roll is used, and, when the heated roll is detached from the base, pressure is instantly removed; however, heat cannot be removed immediately due to heat capacity and thermal conductivity. Therefore, the transfer printing sheet is inevitably released from the pressure of the heated roll before the heat-sensitive adhesive is fully cooled, so that the transfer printing sheet separates from the base, and recessed portions cause defective transfer printing.
An object of the present invention is to provide a transfer printing method for curved surfaces and a transfer printing system for curved surfaces, capable of providing a transfer printing sheet on any three-dimensional curved surface.